JP4402790B2 - Optical position measuring device - Google Patents

Description

ここで
ｎ_i ：第１部分光束の１つの目盛で発生した回折次数
ｎ_i ′：第２部分光束の１つの目盛で発生した回折次数
ＴＰ_i ：各目盛の目盛周期
Ｍ：通過した目盛の数
この際図１にも表されたコリメータ光学系１．２を度外視して、場合によっては、光束のコリメーションに影響し得る光路に他の光学的要素は配設されていないことを前提とする。
【００２２】
測定目盛２．２及び走査目盛１．４を備えた図１の例において、式（１）による走査目盛及び測定目盛の予め設定された目盛周期ＴＰ_M 、ＴＰ_A 及びＭ＝２から副尺周期∩ _Vernierが得られる。
【００２３】
∩ _Vernier＝１／〔（１／ＴＰ_A ）−（１／ＴＰ_M ）〕
この関係から、反射する副尺縞模様の副尺周期∩ _Vernierは、走査目盛及び測定目盛の目盛周期ＴＰ_A 及びＴＰ_M の相違が著しければ著しい程小さくなる。
【００２４】
分かり易く言えば、コリメート照明の場合について上記の分析的に記載された副尺周期∩ _Vernierは、その下に基本的に最後に通過した目盛の平面内に生じる（部分）縞模様の周期であると定義される。
【００２５】
ブロックＢ１〜Ｂ５に対する、図示の実施例における検出器配列１．５の内方にそれぞれ４つの個々の検出器要素が上記の間隔Ｌ _DETで設けられている。隣接する検出器要素は、副尺縞模様の走査の際にそれぞれ９０°だけ位相のずれた部分走査信号を供給する。
【００２６】
従って、ブロックＢ１〜Ｂ５当たりのｋ個の検出器要素の一般的な場合に、隣接する検出器要素から３６０°／ｋ位相のずれた部分走査信号が生じる。
【００２７】
図２の図示から同様に認められるように、相異なるブロックＢ１〜Ｂ５の同一の検出器要素Ｄ１〜Ｄ２０は、互いに接続され又は出力側で伝導的に結合されて、位相の等しい出力信号又は部分走査信号を供給する。最終的にそのように得られる走査信号Ａ₀ 、Ａ ₉₀ 、Ａ ₁₈₀及びＡ₂₇₀ は、出力側で公知の形式及び方法で処理される。このために検出器配列１．５の両縦側には、接触領域が設けられ、接触領域を介して、発生した走査信号Ａ₀ 、Ａ ₉₀ 、Ａ ₁₈₀及びＡ₂₇₀ が取り出されることができる。
【００２８】
そのような検出器配列の代表的な実施例において、走査されるべき２５０μｍの副尺周期が予め設定される。このためにそれぞれ４つの検出器要素を備えた合わせて１０個のブロックが使用され、即ち測定方向Ｘにおける検出器配列の内方の長さＬ_DET ＝１０×２５０μｍ＝２．５ｍｍである。検出器要素のＸ方向の幅は、４７．５μｍであり、Ｙ方向の長さは、１．８ｍｍに選択される。隣接した検出器要素の中心間のＸ方向の距離Ｌ_DET は、６２．５μｍである。
【００２９】
隣接した検出器要素の出力信号間の位相差Δφは一般に次の通りである。
【００３０】
Δφ＝（ｍ₁ ＋ｍ ₂／ｋ）×３６０〔°〕
その際相異なる大きさは次のようになる。
【００３１】
ｍ₁ ＝０、１、２、３、・・・・・
ｍ₂ ＝０、１、２、３、・・・・・
一方図示の実施例において、全部で４つの位相のずれた出力信号Ａ₀ 、Ａ ₉₀ 、Ａ ₁₈₀及びＡ₂₇₀ が検出されかつ処理される場合、本発明の領域内で、検出器要素の数及び若しくは幅又はブロック当たりの相互の間隔を変えることは勿論可能であり、その結果例えば１２０°だけ位相のずれた、更に処理等され得る３つの走査信号が得られる。同様に検出器配列において使用される検出器要素を備えたブロックの数を考慮して、勿論変形可能性が存在する。この形式及び方法で、従って、多くの位相のずれた走査信号が発生され、また走査信号の間の相応した位相関係が調整され得る。他の位相位置の検出器要素と接続されて配設されたある位相位置の多数の接続された検出器要素によって、いわゆる「単一フィールド走査」（Ｅｉｎｆｅｌｄａｂｔａｓｔｕｎｇ）が、副尺縞模様の走査の際にも行われる。そのような単一フィールド走査では、測定目盛の走査された同一の領域から走査信号の位相のずれた全ての信号部分が得られる。測定目盛の局部的な汚れは、それによって全ての信号部分に対して実質的に同様であり、汚れた個所での補間誤差は生じない、即ち実質的に正確な測定システムが得られる。類似の利点は、場合によっては目盛誤差についても挙げられる。各単一フィールド走査の質は、発生した副尺周期に依存する。副尺周期が小さければ小さい程、それだけ位相のずれた全ての信号部分への目盛不正確又は汚れに基づく前記誤差は、均等になる。従ってそのような位置測定装置の寸法では、相応した検出器配列による小さい副尺周期を走査するように努められる。
【００３２】
既にこれまでに述べたように、検出器配列の具体的な構成の他に略図２で示されたように、検出器配列を空間的に本発明による位置測定装置の他の構成部分に関して、検出された走査信号の充分な変調度又は副尺縞模様の充分な対照が得られるように配設されることが重要である。それぞれ最後に通過された又は最後に作用した位置測定装置から検出器平面までの距離Ｚは、特に重要である。本発明による光学的位置測定装置の構成によって、最後に通過された又は最後に作用した目盛では、１つの走査目盛又は１つの測定目盛が対象とされる。この最後に通過された目盛までの距離Ｚは、次に最後に通過された又は最後に作用した目盛を有する平面と検出器平面との間の垂直距離として理解される。
【００３３】
本発明の領域内で、根本的に最後に通過された目盛の距離Ｚの増大に伴って発生した副尺縞模様のコントラストの減少が存在することが認められる。この際使用された走査及び測定目盛の目盛周期が小さければ小さい程かつ副尺縞模様の副尺周期が小さければ小さい程、コントラストの減少は著しい。特に小さい副尺周期を有するそのような高い分解能の位置測定装置では、副尺縞模様の充分なコントラスト、従って走査信号の充分な変調を保証するために、検出器平面の好適な配列の問題が生じる。
【００３４】
しかし本発明によれば、最後に通過された目盛からの特定された距離Ｚ_n におけるコントラストは、再び上昇し、即ち、増大した距離Ｚによっても発生した副尺縞模様の比較的大きなコントラストが生じる検出器平面が存在することが認められる。これらの検出器平面を、公知のトールボット効果に従って副尺トールボット平面と称する。トールボット平面は、コリメート照明された一般的な場合にく最後に通過された目盛からの距離Ｚ_n に存在し、その際Ｚ_n に対して次の式が成立する。
【００３５】
Ｚ_n ＝ｎ×ｄ_VT （式 ２）
ｎについてはｎ＝１、２、３、・・・である。値ｄ_VTを次に副尺トールボット距離と称しかつ次の式（３）により得られる。
【００３６】
ｄ_VT＝（∩ _Vernier×ＴＰ_A ）／λ （式 ３）
この際
ｄ_VT：副尺縞模様の充分なコントラストを有する隣接した副尺トールボット平面の距離
∩ _Vernier：式（１）による走査された副尺縞模様の副尺周期であり、一般に最後に通過された目盛の個所での縞模様の周期である。
ＴＰ_eff ：走査装置の有効目盛周期であり、最後に通過された目盛で生じる充分な強度を有する回折次数の方向を正しく描き、結像システムでは、ＴＰ_eff は一般に最後の目盛の目盛周期に相当し、干渉３格子システムにおける最後の目盛の最後の目盛周期の１／２又は１／３である。
λ：使用された光源の波長
図１の実施例において、ＴＰ_eff ＝ＴＰ_M 、即ち副尺トールボット平面距離ｄ_VTは、式（３）により（∩ _Vernier×ＴＰ_M ）／λとして得られる。
【００３７】
従って式（２）でｎ＝０というあり得ない場合は、最後に通過された目盛の直後に図２による検出器配列が位置決めされ得るような好適な検出器平面が存在することは重要である。このことが、特定の従来の理由から不可能な場合、この実施形態における検出器配列が、本発明によれば、最後に通過された目盛の後方、Ｚ₁ ＝１×（ＴＰ_M ×∩ _Vernier）／λに配設され、ｎ＝１に選択される等である。
【００３８】
この関係の図式的な、尺度は正しくない図示は、図３に示され、図３は、測定目盛Ｍと走査目盛Ａの他に、式（２）及び（３）で使用されているように、種々の幾何学的大きさＴＰ_M 、ＴＰ_A 、∩ _Vernier、Ｚ₁ 及びｄ_VTを示す。更に図３に図示されており、従って周期的距離ｄ_VTにおいて、充分なコントラストをもった好適な検出器平面が得られる。そのように副尺効果に基づいて最後に通過された目盛の直後に副尺縞模様が現れる。しかし伝播する光束は、単一の伝播方向を有する。選択された目盛パラメータに従って種々の回折次数が存在する。そのように最後に通過された目盛で検出器配列の前に−この場合測定目盛Ｍに−回折次数０．の光束が生じるのみならず、後続の検出器配列の方向に伝播する±１．次及び高い回折次数が生じる。干渉によって主として個々の部分副尺縞が発生する副尺効果に基づく個々の回折次数の細分割は無視される。そのような回折次数が遮断した場合、重ね合わされた全ての回折次数を有する全光束を考慮した場合と同一の副尺縞模様が生じる。各回折次数は、目盛方向Ｘにおける部分副尺縞模様を有する。一方最後に通過された目盛Ｍの平面には、種々の部分副尺縞模様の位相の正しい重ね合わせが存在する場合、相異なる伝播方向に基づいて続いて位相関係が変わる。しかし最後の目盛Ａからの前記距離Ｚ_n には、再び充分なコントラストの副尺縞模様が存在する、そのわけは相異なる回折次数の部分副尺縞模様が、再び位相正しく重ねられるからである。
【００３９】
実際上この際最後の目盛Ｔからの距離Ｚ₁ 、Ｚ₂ を有する検出器平面は特に重要である、そのわけはｎの値が大きい場合、場合によっては最適ではないコリメート照明が、追加的に否定的に評価され、即ちコントラストが減少するからである。
【００４０】
記載の効果は、トールボット効果として公知の格子の公知の自動結像に極めて類似する。従って副尺縞システムの上記の自動結像は、副尺−トールボット効果と称され、大きさｄ_VTを、副尺タールボット距離と称する。
【００４１】
次に本発明による光学的位置測定装置の第２実施例のパラメータのための具体的な数値が付与され、この実施例は、同様に結像システムとして形成されかつ図１の例と類似の基本構造を有する。この際結像システムは、副尺効果を除き発生した回折次数の分離が必要ではないように特定されている、そのわけは個々の回折次数の言うに値する全ての強度変調は、略同位相であり従って消失しないからである。一般にそのような結像システムの最後に通過される目盛は、振幅格子として形成されている。
【００４２】
本発明による位置測定装置の第２実施変形において、ＬＥＤ又は半導体レーザが光源として使用され、光源は波長λ＝８６０ｎｍの光を発する。光源の光軸は、走査板の法線に対して目盛範囲縦軸線の方向に角度ε＝３０°だけ傾斜して配置される。光源から発せられる光束は、先ず、位相板として形成されかつウエブ及び隙間の形に交互に配設された目盛領域を有する透明な走査板上の走査目盛上に達する。走査目盛の位相格子は、ＴＰ_A ＝３７．０４μｍ、位相角φ＝π並びにウエブ−目盛周期比τ＝０．５を有し、即ちウエブは測定方向Ｘに隙間の幅を有する。位相格子上に現れる光束が種々の回折次数に分解された後、回折された光束は反射測定目盛上に達する。これは、交互に配設された反射する線と反射しない隙間とを備えた振幅格子として形成されかつ目盛周期ＴＰ_M ＝２０μｍ≠ＴＰ_A ／２並びに線−目盛周期比τ＝０．５を有する。そこから更に光束は、走査板の方向に反射され、そこで光束は走査板の透明な窓を通りかつ最後に検出器配列上に現れる。そこで生じた副尺縞模様が検出され、副尺縞模様は式（１）による記載の変形では、副尺周期∩ _Vernier＝１／（２／ＴＰ_A ）−（１／ＴＰ_M ）を有する。この際検出器配列は、最後に通過された目盛からＺ₁ ＝（∩ _Vernier×ＴＰ_M ）／λの距離に配設されておりかつ図２による実施例と類似して形成されることができ、その結果出力側で最終的に所望の数の位相のずれた走査信号が得られる。一般に検出器配列はこの際、１２０°位相のずれた３つの走査信号又は９０°だけ位相のずれた走査信号が得られるように設定されている。検出された走査信号の信号周期が、この実施例では他の測定目盛周期ＴＰ_M に相応する。第１実施例に完全のために既にこの個所に次に説明する両値η及びβが付与され、η＝０、β＝１である。
【００４３】
一方これまでに、結像位置測定装置との関係が説明されたように、干渉位置測定装置の形の他の実施例の次の記載によって、本発明による構成がそのようなシステムにも適用されることが明らかにされる。
【００４４】
図４は、干渉位置測定装置として形成された本発明による光学的位置測定装置の第３実施例の図式的側面図を示す。位置測定装置は、更に測定尺１２に対して測定方向Ｘに移動可能に配設された走査ユニット１１を有し、その際測定尺は、測定目盛支持体１２．１並びにその上に配設された測定目盛１２．２から成る。測定方向Ｘは、この図示において図平面に対して垂直に向けられている。ＬＥＤ又は好適な半導体レーザとして形成された光源１１．１は走査ユニット１１に属し、その光軸は、線方向において透明な走査板１１．３の表面上の法線に対して角度εだけ傾いて配置されている。光源１１．１に、コリメータ光学系１１．２に後続しており、このコリメータ光学系を、光束が、この実施例においては走査板１１．３の表面上に配設された走査目盛１１．４ａの第１部分領域上に現れる前に、通過する。走査目盛１１．４ａは、前記実施例のように位相格子として形成されておりかつ走査−目盛周期ＴＰ_A ＝１５．７５μｍ、位相角φ＝π並びにウエブ−目盛周期比τ＝０．５を有する。種々の格子パラメータの定義に関して上記の実施例が参照される。走査目盛１１．４ａでは、現れた光束の種々の回折次数への分割が行われ，続いて回折された光束は、反射測定目盛Ｍ上に現れる。反射測定目盛は同様に、位相格子として形成されておりかつ目盛周期ＴＰ_M ＝８μｍ≠０．５×ＴＰ_A 、位相角φ＝π並びにウエブ−目盛周期比τ＝０．５を有する位相格子として形成されている。走査板１１．３の方向における更に回折された光束の方向に行われる反射後、光束は走査目盛の第２部分領域上に現れ、部分領域に従って種々の分割された光束の相会が行われる。この場合最後に通過された目盛を表す走査目盛１１．４ｂを通過した後、副尺周期∩ _Vernier＝１／〔（４／ＴＰ_A ）−（２／ＴＰ_M ）〕を有する副尺縞模様が生じる。副尺周期∩ _Vernierは、既に上に記載した式（１）から得られる。前記両実施例のように、既にこの個所で次に説明されるべき両値、η及びβが与えられており：η＝０．５、β＝１である。
【００４５】
改めてこの例において種々の、相異なる回折方向に伝播する部分副尺縞模様の位相の正しい重ね合わせのために最後の目盛からの所定の距離Ｚ_n の状態のみが重要である。この距離において充分なコントラストをもつ副尺縞模様が存在しかつ検出器配列１１．５によって検出されることができる。検出器配列１１．５は、暗示されたように図２の例における構成に相応する基本的構造を有する。最後に通過された目盛から光学的検出器平面までの距離Ｚ_n のために、部分副尺縞が既に最後に通過された目盛の平面内で互いに位相がずらされていることが考慮されなければならない。この位相差は、相応して変更された距離Ｚ_n によって補償されなければならない。これには次の式（４）が適用される。
【００４６】
Ｚ_n ＝（ｎ＋η）×ｄ_VT （式４）
この際ｎ＝０、１、２、３、・・・である。
【００４７】
ｄ_VT：式（３）によって特定され、副尺縞模様の充分なコントラストを有する隣接した検出器平面又は副尺タールボット平面の距離
η：最後に通過された目盛で種々の方向に現れる部分副尺縞模様の３６０°の分数の位相差であり、この位相差は、最後に通過された目盛の平面内の各個所に発生した回折次数相互間の位相差である。図４の上記実施例の場合に、位相差は１８０°であり、即ちηは、η＝０．５；一般に０≦η＜１である。
【００４８】
値ｄ_VTには、即ち副尺トールボット距離のために、この例ではｄ_VT＝（∩ _Vernier×ＴＰ_M ）／λである。従って最後に通過された目盛の直後に式（４）によれば、走査信号の全く又は僅かだけの変調又は副尺縞模様の僅かなコントラストのみが予期される。可能な第１の検出器平面は、０≦η＜１で、ｎ＝０、従って距離Ｚ₀ に生じる。
【００４９】
一般に本発明によれば、結像システムでは、η＝０かつｎ＞０に選択され、これに対して干渉システムではη≠０かつｎ＝０、１、２、３、・・・である。
【００５０】
図示の実施例とは異なり、走査目盛１１．４ａ、１１．４ｂが、走査板１１．３の光源に向いた上面上には配設されておらず、走査目盛１１．４ｂが、走査板１１．３の測定目盛１２．２に向いた下面上に配設されている場合、走査板１１．３の厚さの好適な選択によって、検出器配列１１．５が走査板１１．３の直接上面上に取り付けられ、このことは、ｎ＝０の場合に相応する。そのような実施形態において、走査板１１．３上での検出器配列１１．５の接触も可能である。このことは、例えば公知のチップ−オン−ガラス−技術及び又はフリップチップ技術で行われることができる。
【００５１】
検出された走査信号の信号周期ＳＰは、この実施例においてはその他通常測定目盛ＴＰ_M の半分、即ちＳＰ＝ＴＰ_M ／２＝４μｍに相応する。
【００５２】
次に図４の実施例の変形された形態が記載され、即ち干渉システムとして形成された本発明の第４実施例を説明する。走査格子１１．４ａ、１１．４ｂは、改めて位相格子として形成されておりかつ目盛周期ＴＰ_A ＝８μｍ、位相角φ＝（２／３）並びにウエブ−目盛周期比τ＝０．３４を有する。測定目盛１２．２は、目盛周期ＴＰ_M ＝７．８７４μｍ≠ＴＰ_A 、位相角φ＝π及びウエブ−目盛周期比τ＝０．５を有する。副尺周期∩ _Vernierは、式（１）から∩ _Vernier＝１／〔（２／ＴＰ_A ）−（２／ＴＰ_M ）〕として得られる。値ηとしては、この場合η＝１／３である。次に説明すべき値βは、更にβ＝１である。
【００５３】
本発明による干渉による光学的位置測定装置の他の実施形態は従って本発明の領域内の一括して第５の実施例は、図５に表される。図示の位置測定装置は、更に測定目盛２２．２に対して測定方向Ｘに移動可能に配設されている走査ユニット２１を有し、その際測定方向Ｘは改めて図平面に対して垂直に向けられている。特別に有利な実施形態において、測定目盛２２．２は、可撓性帯状測定尺として形成されている。走査ユニット２１の側にＬＥＤ又は好適な半導体レーザとして形成された光源２１．１が設けられ、その光軸は、透明な走査板２１．３の表面に対して角度εだけ傾けて配置されている。光源２１．１は、コリメータ光学系に後続して配設され、コリメータ光学系は、光束が走査板２１．３の透明で、光学的に有効ではない領域を通過する前に、光源２１．１から発せられた光束を透過させる。走査板２１．３を通過後、光束は、反射位相格子として形成された測定目盛２２．２上に初めて達する。測定目盛は、目盛周期ＴＰ_M ＝１６μｍ、位相角φ＝π及びウエブ−目盛周期比τ＝０．５を有する。測定目盛２２．２から光束が走査板２１．３の方向でそこに配設された走査目盛２１．４上に反射し、走査目盛は、走査板２１．３の上面の内方に配設されている。設けられた走査目盛２１．４は、目盛周期ＴＰ_A ＝７．８７４μｍ≠０．５×ＴＰ_M 、位相角φ＝π及びウエブ−目盛周期比τ＝０．５の反射する位相格子として形成されている。種々の格子パラメータの定義に関して、改めて上記実施形態が参照される。走査目盛２１．４によって回折された光束の測定目盛２２．２方向への反射が行われ、そこから更に第２の反射が走査板２１．３の方向に行われる。走査板２１．３は、最後に通過した目盛２２．２に従って生じる副尺縞模様が検出器配列２１．５を介して検出される前に、測定目盛２２．２から来る光束によって透明の領域を通過される。検出器配列は本発明によれば、更に好適な検出器平面上に配設されている。その際検出された副尺縞模様は、副尺周期∩ _Vernierを有し、副尺周期∩ _Vernierは、式（１）によれば、∩ _Vernier＝１／〔（４／ＴＰ_A ）−（２／ＴＰ_M ）〕として上記式（３）から得られる。更にβ＝１、η＝１／２である。
【００５４】
種々の部分副尺縞模様の位相正しい重合わせに至る最後の目盛からの距離Ｚ_n に対して、この場合も上記式（４）でη＝１／２である。相応してこの平面内でも検出器配列２２．５等の配列が行われる。更に最後に通過された目盛の直後に、この場合測定目盛２２．２がある場合、検出された走査信号の僅かな変調のみが予期される。ｎ＝０の第１の基本的に可能な走査平面は、この構成において同様に最適ではないことが実証される、そのわけは可能な走査平面は、所定のパラメータでは測定目盛２２と走査板２１．３の間に位置するからである。この理由から検出器平面内の検出器配列２１．５は、最後に通過された目盛から距離Ｚ₁ ＝１）を有する検出器平面に位置決めされ、そこで本発明によれば充分なコントラストの副尺縞模様が検出される。検出される走査信号の信号周期ＳＰは、この実施例ではＳＰ＝ＴＰ_M ／４である。
【００５５】
図５による実施形態の他の変形において、即ち本発明の第６の実施例において、次のパラメータが選択される。位相格子として形成された測定目盛２２．２に対して目盛周期ＴＰ_M ≠ＴＰ_A ；位相角φ＝２／３π及びウエブ−目盛周期比τ≒０．３４が適用される。同様に位相格子として形成された走査目盛２１．４としてＴＰ_A ≠ＴＰ_M ；位相角φ＝π及びウエブ−目盛周期比τ≒０．５及び更にβ＝１、η＝１／３が適用される。
【００５６】
走査板２１．３の側の走査目盛２１．４の配列に関して更に種々の可能性がある。走査目盛２１．４が直接走査板２１．３の上面上に配設され得る場合、このことは僅かな汚れの可能性に繋がる。しかし同様に走査板２１．３の相応した厚さの選択では走査板２１．３の測定目盛に向いた側に走査目盛２１．４を配置することも可能である。この変形では、検出器配列２１．５は直接走査板２１．３の上面上に配設されることができる。
【００５７】
次に同様に本発明による構想を基礎とした光学的位置測定装置の他の実施変形を述べる。例えば図５の実施例における測定目盛２２．２は、回転シリンダの内側又は外側に湾曲した形で配設されることができる。この際シリンダの回転軸線は、Ｙ方向に向けられている。そのような変形において、走査されるべき副尺縞模様の検出器平面内の拡大又は縮小は、測定目盛２２．２の湾曲した配置に基づいて行われる。シリンダ外面上に測定目盛を配置する場合、拡張が行われ、シリンダ内面上に配置する場合には、相応した縮小が行われる。この光学的効果は、湾曲した測定目盛の場合には、例えば光路における任意に集束させ又は拡散される光学的要素に起因するコリメートではない光路を有する他の全ての場合と同様に、上記式（３）における湾曲した測定目盛の場合が考慮される。このために部分副尺縞模様周期の伝達又は拡大を最後に通過された目盛の個所から検出器平面までの部分副尺縞模様周期の伝達及び拡大を描く拡大ファクタ又は又は修正ファクタβが導入される。従って一般的な式（３）が得られる。
【００５８】
ｄ_VT＝（β×∩ _Vernier×ＴＰ_eff ）／λ （式３）
又はｄ_VT＝β×ｄ_VT0 が成立ち、その際
ｄ_VT0 ＝（∩ _Vernier×ＴＰ_eff ）／λ
であり、かつ
∩ _Vernier：最後に通過された目盛の個所での部分副尺縞模様の副尺周期である。
【００５９】
一般的な式（３′）に敷衍する拡大ファクタβは、勿論本発明による位置測定装置の内方の所定の幾何学的値に依存する。この関係において、図６が参照され、図６は、ファクタが特定される重要な値の説明に役立つ。図６には副尺縞模様∩ _Vernierを有する部分副尺縞模様がその平面内に位置する最後に通過された目盛Ｔの他に、更に目盛Ｔからの距離Ｚ_n に検出器平面が示され、その検出器平面に存在する拡散された光束に基づいて、ファクタβでけ拡大された副尺縞模様が存在する。更に図６に示された点Ｑは、この場合光束又は副尺縞模様の虚光源点又は実光源点とみなされる。従って距離Ｚ_Q は、最後に通過された目盛Ｔからの実光源点又は虚光源点の距離を与える。β＞１、即ち副尺縞模様の拡大の場合、距離Ｚ_Q は、Ｚ_Q ＞０；β＜１の場合、即ち縞模様の理論的縮小の場合にＺ_Q ＜０である。中央の区間の原則によれば、そのような幾何学的寸法では、拡大ファクタ又は修正ファクタβは次のようになる。
【００６０】
β＝（Ｚ_n ＋Ｚ_Q ）／Ｚ_Q
シリンダ外面上の測定目盛の配置の上記選択された場合、ファクタβ＞１が選択され、これに対してシリンダ内面上の測定目盛の配置の場合にβ＜１が選択される。
【００６１】
式（４）並びに上記の説明された式（３′）から、本発明によるシステムに対して有効な全ての式（５）が適用され、この式（５）から検出器平面の位置又は最後に通過された目盛からの距離Ｚ_Q が求められる。
【００６２】
１／Ｚ_n ＋１／Ｚ_Q ＝１／〔（ｎ＋η）×ｄ_VT0 〕（式５）
式（５）中の値Ｚ_Q 、ｎ及びηの意味は、既に上に説明された。同様に値ｄ_VT0 の定義は、すでに説明され、その際その定義において副尺縞周期∩ _Vernierが介入する。一方議論された結像システムでは、非コリメート照明の場合又は光路に光学的要素を使用する場合、光路は光束の拡散に影響し、副尺周期∩ _Vernierの明らかな分析的表現の記載は式（１）に類似して不可能である。副尺周期∩ _Vernierは、特に光学的条件に適合される関係によってのみ付与される。選択的にそのようなシステムでの副尺周期∩ _Vernierの特定は、いわゆる「光線追跡）のような数値的な方法が可能である。従って基本的には、一般的な式（５）における副尺周期の下に最後に通過された目盛の個所での部分副尺縞模様の周期が理解される。
【００６３】
式（５）は、既に述べたように、非コリメート照明の場合にもコリメート照明の場合にも有効である。コリメート照明の場合に値Ｚ_Q はＺ_Q ＝∞として、即ちβ＝１に選択され、従って式（５）は上記の式（４）と同一である。逆に非コリメート照明の場合、値Ｚ_Q は最終的に、即ちＺ_Q ≠∞かつβ≠＝１である。
【００６４】
次に値Ｚ_Q が式（５）でＺ_Q ＝（ｎ＋η）×ｄ_VT0 として選択され、ここにｎ＝１、２、・・・・である場合が述べられる。副尺縞模様は最後に通過された目盛からの距離Ｚ_n ＝∞に生じる。実際上検出器配列は、後続の目盛に後続する集束するレンズの焦点平面内に位置決めされなければならない。
【００６５】
基本的に勿論最後に通過された目盛には、いわゆるリレー光学系が後続され、この光学系は、式（５）により得られる検出器平面の像を他の平面内に生じさせる。
【００６６】
続いて干渉システムの場合に導入された式（５）が、値ηの相応した選択の際に結像位置測定装置にも適用され、この場合η＝０に選択する。
【００６７】
このことは、上記の式（３′）と（５）が一般的有効性を有しかつ相異なるパラメータの相応した選択によって本発明による光学的位置測定装置について述べた結像及び干渉の変形が具体的に記載されることができる。この際これらの式は、冒頭に記載されたドイツ国特許出願第１９５２７２８７号明細書による結像システムのような光学的位置測定装置の公知の場合をも記載する。そこでは殆ど最後に通過された目盛の直後に検出器平面が位置決めされかつ得られる副尺縞模様が検出され、即ちパラメータｎ及びηは、そのような位置測定装置ではｎ≒０かつη＝０が選択される。本発明による光学的位置測定装置にとって一般的に有効な式（３）及び（５）におけるパラメータｎ及びηは、ｎ＞０又はη≒０に選択される。
【００６８】
基本的にこの個所で、勿論各検出器平面の正確な位置に関する幾分の公差が存在する。上記式により得られる理想位置からの僅かな偏倚のある場合でも場合によっては充分な強度変調が達成されることができる。
【００６９】
更に本発明の領域内で、例えば使用された目盛の１つが二次元目盛として形成され従ってモアレ縞の方向に偏倚した横断的な回折次数が生じる場合に、いわゆるモアレ縞の形の測定方向に対して垂直に経過する周期的縞模様の検出も可能である。選択的にモアレ縞の発生は勿論公知の形式及び方法で達成され、その際使用された目盛は、所定の角度だけ互いに捩じられて配設される。
【００７０】
従って、本発明が種々の実施形態において形成され得るような一連の可能性が存在する。従って実施例の上記記載は、勿論本発明思想の完璧な理解までには到らしめないであろう。
【図面の簡単な説明】
【図１】図１は、結像位置測定装置として形成された、本発明による位置測定装置の第１実施例の基本的構成を示す図である。
【図２】図２は、走査された副尺縞模様と関連した図１による本発明による光学的位置測定装置の実施例の検出器平面を表す図である。
【図３】図３は、結像される位置測定装置における検出器平面の最適の位置決めとの関連を説明するための図式図である。
【図４】図４は、干渉位置測定装置として形成された、本発明による位置測定装置の第３実施例の図式図である。
【図５】図５は、干渉位置測定装置として形成された、本発明による位置測定装置の第５実施例の図式図である。
【図６】図６は、非コリメート照明の場合の状況を説明するための図式図である。
【符号の説明】
１ 走査ユニット
１．１ 光源
１．４ 走査目盛
１．５ 検出器配列
２．２ 測定目盛
１１ 走査ユニット
１１．１ 光源
１１．４ａ 走査目盛
１１．４ｂ 走査目盛
１１．５ 検出器配列
１２．２ 測定目盛
２１ 走査ユニット
２１．１ 光源
２１．４ 走査目盛
２１．５ 検出器配列
２２．２ 測定目盛[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical position measurement apparatus suitable for precise measurement of relative positions of objects that are movable relative to each other.
[0002]
There is an incremental position measuring device in which a scale provided on the measurement scale side and the scanning side, that is, a measurement scale, and one or a plurality of scanning scales have different scale periods (pitch). When these graduations are illuminated by a light source, a periodic stripe pattern is produced in the detector plane that can be detected by a suitable detector array. In this case, the periodic stripe pattern is generated by different scales in the optical path and the exchange action of the light beams emitted from the light source. Hereinafter, this stripe pattern is referred to as a vernier stripe pattern, and the period of the stripe pattern is specified by the vernier period.
[0003]
[Prior art]
At this time, in relation to the generation format and method of the vernier stripe pattern, on the one hand, a so-called imaging position measuring device having a relatively large scale period on the measuring scale side and the scanning side is targeted. The obtained vernier stripe pattern is produced substantially as a shadow. These systems generally have a measurement scale as well as a scanning scale. For this purpose reference is made, for example, to German Patent Application No. 19527287 or German Patent Application No. 1798368. The scanning of the striped pattern obtained with a relatively large vernier period is performed by a quadrant detector that is suitably arranged. Reference is further made to German Patent 2,653,545.
[0004]
On the other hand, the resulting vernier stripe pattern is also generated in principle by means of an interferometric position measuring device, in which the measuring scale side and the scanning side have very small scale periods. A vernier pattern in the scanned detector plane arises in such a measuring device from a partial beam that is diffracted by the used graduation and arrives due to interference. Reference is made to German Patent No. 2714324 for this relationship.
[0005]
[Problems to be solved by the invention]
An imaging position measuring device and an interference position measuring device for generating a vernier stripe pattern that satisfies a specific condition should be provided. As such, it should basically be ensured that a sufficiently good modulated scanning signal is obtained in the case of relative movement from scanning with a vernier stripe pattern. Any contamination that may occur on the surface of the measuring scale should not affect the scanning signal as much as possible. In addition, some flexibility with respect to the position of the detector plane is required, because of the structural constraints, the detector plane is not necessarily placed immediately after the last graduation of the position measuring device. Because you can't. The latter is particularly important in view of a compactly configured scanning unit. Furthermore, with a small period of vernier stripes in the imaging system, the distance between the last passed graduation and the detector plane should be extremely small. The reason is the higher diffraction orders leading to a slight contrast fringe image. However, such a small distance is difficult to achieve in practice, and the bond wires of each detector element protruding on the detector may be damaged. In the case of an interference system, spatial separation by a frequently occurring diffraction order lens is required. However, in such a position measuring apparatus, a vernier stripe pattern does not occur even when the scales placed on the focal plane of the lens have different scale periods.
[0006]
[Means for Solving the Problems]
An optical position measuring device that satisfies these requirements is the object of claim 1.
[0007]
Advantageous embodiments of the position measuring device according to the invention result from the measures in the dependent claims.
[0008]
The measures according to the invention, in particular in terms of the detector arrangement, ensure that the movement-dependent scanning signal is generated with high resolution, not sensitive to contamination or sensitive to disturbances. This is ensured on the basis of a correspondingly arranged detector arrangement, since in some cases the contamination on the measurement scale acts more uniformly on different, out-of-phase signal parts. It is.
[0009]
  Furthermore, some flexibility in the recognition of the optical position of the detector plane takes into account different structural conditions. Thus, for example, it is no longer unconditionally necessary to place the detector arrays immediately after the last passed graduation. It has been recognized that the present invention provides another possibility for the arrangement of detector elements to provide a sufficiently good modulated scan signal in a similar case. This ultimately gives the possibility of realizing a very compactly configured scanning unit which simultaneously achieves a high signal contrast or a high degree of modulation.
[0010]
Similarly, an interference position measuring device that supplies a vernier stripe pattern on the scanning side in recognition of the optical position of the detector plane can be provided. The advantage of the interferometric position measuring device according to the present invention, in which different diffraction orders are not separated, is that the entire signal part is similarly affected when the diffraction characteristics should be changed over the length of the measurement scale. Will be done.
[0011]
In this manner and method, signals having a phase difference of 90 ° each are generated in the interference system, and the signals can be further processed by standard electronic evaluation equipment. Due to the very accurate generation of the push-pull signal, the second harmonics that otherwise cause errors during the subsequent signal interpolation are also lost.
[0012]
Of course, the concept according to the invention applies to both rotational position measuring devices and linear position measuring devices. A possible position measuring device can also constitute a position measuring device that operates with reflected or transmitted light according to the invention.
[0013]
Other advantages and other details of the optical position measuring device according to the invention can be taken from the following description of several embodiments on the basis of the attached drawings.
[0014]
【Example】
  A first embodiment of the optical position measuring device according to the invention will now be described with reference to FIGS. FIG. 1 shows a schematic side view of the imaging optical position measuring device. The optical position measuring device consists essentially of a scanning unit 1 and a measuring rule 2 with a measuring scale 2.2 and a scale support 2.1. The scanning unit 1 and the measuring scale 2 are coupled to two objects that are movable relative to each other whose relative positions are to be determined. For example, tools and workpieces in machine tools that are numerically controlled at that time are targeted. In the embodiment shown, the scanning unit 1 and the measuring scale 2 are movable relative to each other in the measuring direction X, with X being oriented perpendicular to the drawing plane. The scanned measurement graduation 2.2 is alternately arranged in the measurement direction X, and on the measurement graduation 2.1 having a partial area that reflects and a non-reflecting partial area whose longitudinal axis is directed in the Y direction. The known reflected light incremental scale. Scale period TP of measurement scale 2.2_MAs a result, the width of the reflected partial area in addition to the width of the non-reflected partial area in the measurement direction X is understood. The scanned measurement graduation 2.2 is thus formed in this embodiment as a pure amplitude grating and has a graduation period TP._MTP_M= 20.00 μm, the partial area-scale period-ratio is τ, that is, the ratio of the width of the reflected partial area to the scale period in the measurement direction X is τ = 0.5.
[0015]
The scanning unit 1 which can move relative to the measurement graduation 2.2 comprises a light source 1.1, a collimator optical system 1.2, a scanning graduation period TP in the illustrated embodiment._AA transparent scanning plate 1.3 with a scanning scale of 1.4 and a detector array 1.5. The optical axis of the light source 1.1 is inclined with respect to the normal on the scanning plate 1.3 within an angle ε = 30 ° in the drawing plane. The scanning scale 1.4 of this embodiment is formed as a phase grating and has a scale period TP._A= 18.52 μm (hence TP_M≠ TP_A), The web / scale period ratio τ is selected to be τ = 0.5, and the phase angle φ is φ = π / 2. Already at this point for the sake of complete understanding, the dimensions η and β described in detail below are given in this example, which are η = 0, β = 1 in the case of an imaging system with collimated illumination. is there.
[0016]
A light beam emitted from the light source 1.1 first passes through the transparent scanning plate 1.3 after being collimated by the collimator optical system, passes through the phase grating-scanning scale 1.4, and is reflected on the measurement scale. Appears on 2.2. From there, the light beam is reflected in the direction of the scanning plate 1.3 and is optically uncharacteristic adjacent to the inherent scanning scale 1.4 before it reaches the detector array 1.5 in the detector plane. Pass through the scanning plate 1.3 in a transparent window. So, they are arranged later-not shown-detection of scanning signals modulated in dependence on periodic fringes or movement and possibly preprocessing of these signals before being sent to the evaluation unit Is done.
[0017]
The essential measures according to the present invention will be described with reference to FIG. FIG. 2 shows, in a schematic form, the part of the detector array 1.5 of the optical position measuring device in the detector plane and the intensity distribution of the vernier pattern scanned thereby. The detector array 1.5 comprises a plurality of photosensitive detector elements D1 to D20 arranged adjacent to each other in the measuring direction X. The individual detector elements D1 to D20 all have the same dimensions in the form of a narrow square, whose longitudinal axis is oriented in the detector plane in the Y direction, ie perpendicular to the measuring direction X. ing. Preset length L of detector array 1.5_DET20 individual detector elements D1 to D20 are collectively arranged in the measurement direction X, and these are grouped into five groups. Each block B1-B5 has a length ∩ in the measurement direction X in the illustrated embodiment with collimated illumination._VernierThis length corresponds to the period of the generated vernier pattern in the detector plane, ie L_DET= K × ∩_VernierIn this case, k = 5 in the illustrated example. Therefore value ∩_VernierIs then referred to as the vernier period (∩_VernierAre described in FIGS. 2 and 3).
[0018]
In general, N detector elements thereby have a distance β × ∩_VernierIn this case, non-collimated illumination can possibly be taken into account for the correction factor β, which will be explained in more detail later. In the above case, the collimated illumination is therefore β = 1, whereas in the case of non-collimated illumination, β ≠ 1, and the correct introduction of the correction factor β is made accordingly in the specification.
[0019]
The spacing between adjacent detector elements D1-D20 is then L_DETAnd in the general case L_DET= (N + Δφ / 360 °) × ∩_Vernierbecome. In this case, n = 0, 1, 2, 3,..., While Δφ represents the phase difference between the detected signals of adjacent detector elements. In the illustrated embodiment, L_DET= 1/4 x ∩_VernierThat is, n = 0 and Δφ = 90 °.
[0020]
The vernier period ∩_VernierComprises a plurality of measuring graduations and / or scanning graduations, hereinafter referred to simply as graduations, and a preset scale period TP corresponding to different graduations of the general form according to the following equation (1)_iIt is obtained in the case of collimated illumination of an optical position measuring device with
[0021]
[Outside 1]

here
n_i: Diffraction order generated at one scale of the first partial light beam
n_i': Diffraction order generated at one scale of the second partial light beam
TP_i: Scale interval of each scale
M: Number of scales passed
In this case, it is assumed that the collimator optical system 1.2 shown in FIG.
[0022]
In the example of FIG. 1 with the measurement graduation 2.2 and the scanning graduation 1.4, the preset graduation period TP of the scanning graduation and the measurement graduation according to the formula (1)_M, TP_AAnd M = 2 from vernier period ∩_VernierIs obtained.
[0023]
∩_Vernier= 1 / [(1 / TP_A)-(1 / TP_M)]
From this relationship, the vernier period of the reflective vernier stripe pattern_VernierIs the scale interval TP of the scanning scale and measurement scale_AAnd TP_MThe more significant the difference is, the smaller it becomes.
[0024]
To put it simply, the above-mentioned analytically described vernier period ∩ for the case of collimated illumination._VernierIs defined as the period of the (partial) striped pattern that occurs in the plane of the scale that has passed through it most recently.
[0025]
For each of the blocks B1 to B5, four individual detector elements are arranged on the inner side of the detector array 1.5 in the illustrated embodiment, with the spacing L described above._DETIs provided. Adjacent detector elements provide partial scan signals that are each 90 degrees out of phase during scanning of the vernier stripe pattern.
[0026]
Thus, in the general case of k detector elements per block B1-B5, partial scan signals that are 360 ° / k out of phase from adjacent detector elements are produced.
[0027]
  As can also be seen from the illustration of FIG. 2, the same detector elements D1 to D20 of the different blocks B1 to B5 are connected to each other or conductively coupled on the output side, so that the output signals or parts are of the same phase. Supply a scanning signal. The scanning signal A thus finally obtained₀, A₉₀, A₁₈₀And A₂₇₀Are processed in a known format and manner on the output side. For this purpose, contact areas are provided on both longitudinal sides of the detector array 1.5, and the generated scanning signal A is transmitted through the contact areas.₀, A₉₀, A₁₈₀And A₂₇₀Can be taken out.
[0028]
In an exemplary embodiment of such a detector array, a 250 μm vernier period to be scanned is preset. For this purpose, a total of 10 blocks, each with 4 detector elements, are used, ie the inner length L of the detector array in the measuring direction X_DET= 10 × 250 μm = 2.5 mm. The width of the detector element in the X direction is 47.5 μm and the length in the Y direction is selected to be 1.8 mm. The distance L in the X direction between the centers of adjacent detector elements_DETIs 62.5 μm.
[0029]
The phase difference Δφ between the output signals of adjacent detector elements is generally as follows:
[0030]
Δφ = (m₁+ M₂/ K) × 360 [°]
In this case, the different sizes are as follows.
[0031]
  m₁= 0, 1, 2, 3, ...
  m₂= 0, 1, 2, 3, ...
  On the other hand, in the illustrated embodiment, a total of four out-of-phase output signals A₀, A₉₀, A₁₈₀And A₂₇₀Is detected and processed, it is of course possible to vary the number and / or width of the detector elements or the mutual spacing per block within the region of the invention, so that they are out of phase by eg 120 °. Three scanning signals that can be further processed are obtained. There is of course a possibility of deformation in view of the number of blocks with detector elements used in the detector array as well. In this manner and method, therefore, a number of out-of-phase scan signals can be generated and the corresponding phase relationship between the scan signals can be adjusted. By means of a number of connected detector elements at one phase position arranged in connection with detector elements at other phase positions, a so-called “single field scan” is carried out during scanning of the vernier pattern. Also done. In such a single field scan, all signal portions having a phase shift of the scanning signal are obtained from the same scanned area of the measurement scale. The local contamination of the measurement graduation is thereby substantially the same for all signal parts and no interpolation error occurs at the contamination, i.e. a substantially accurate measurement system is obtained. Similar advantages are also noted for scale errors in some cases. The quality of each single field scan depends on the generated vernier period. The smaller the vernier period, the more uniform the error due to scale inaccuracies or contamination on all signal portions that are out of phase. Thus, with the dimensions of such a position measuring device, an effort is made to scan a small vernier period with a corresponding detector arrangement.
[0032]
As already mentioned above, in addition to the specific configuration of the detector array, as shown schematically in FIG. 2, the detector array is spatially detected with respect to other components of the position measuring device according to the invention. It is important that they be arranged so as to obtain a sufficient degree of modulation of the scanned signal or a sufficient contrast of the vernier pattern. The distance Z from the last passed position measuring device to the detector plane, respectively, is particularly important. With the configuration of the optical position measuring device according to the invention, the last passed or last activated scale is one scanning scale or one measuring scale. This distance Z to the last passed graduation is understood as the vertical distance between the plane having the next last graduation or the last acted graduation and the detector plane.
[0033]
Within the region of the present invention, it can be seen that there is a decrease in the contrast of the vernier stripe pattern that occurred with an increase in the distance Z of the graduation that was fundamentally last passed. In this case, the smaller the scale period of the scanning and measurement graduation used and the smaller the vernier period of the vernier stripe pattern, the more significant the reduction in contrast. Especially in such a high resolution position measuring device with a small vernier period, the problem of the preferred alignment of the detector planes in order to ensure sufficient contrast of the vernier stripes and thus sufficient modulation of the scanning signal. Arise.
[0034]
However, according to the invention, the specified distance Z from the last passed graduation_nIt can be seen that there is a detector plane in which the contrast at is increased again, i.e. a relatively large contrast of the vernier stripe pattern also produced by the increased distance Z. These detector planes are referred to as vernier Talbot planes according to the known Talbot effect. The Talbot plane is the distance Z from the last graduation in the general case of collimated illumination._nIn that case Z_nThe following formula is established.
[0035]
Z_n= N × d_VT          (Formula 2)
For n, n = 1, 2, 3,. Value d_VTIs then referred to as the vernier Talbot distance and is obtained by the following equation (3).
[0036]
d_VT= (∩_Vernier× TP_A) / Λ (Formula 3)
On this occasion
d_VT: Distance between adjacent vernier Talbot planes with sufficient vernier stripe contrast
∩_Vernier: The vernier period of the scanned vernier stripe pattern according to the formula (1), generally the period of the stripe pattern at the last graduation.
TP_eff: The effective graduation period of the scanning device, which correctly draws the direction of the diffraction order with sufficient intensity that occurs in the graduation that was passed last._effIs generally equivalent to the graduation period of the last graduation and is 1/2 or 1/3 of the last graduation period of the last graduation in an interferometric three-grating system.
λ: wavelength of the light source used
In the embodiment of FIG._eff= TP_MThat is, the vernier Talbot plane distance d_VTIs given by (3) (∩_Vernier× TP_M) / Λ.
[0037]
Therefore, if n = 0 is not possible in equation (2), it is important that there is a suitable detector plane in which the detector array according to FIG. 2 can be positioned immediately after the last passed scale. . If this is not possible for certain conventional reasons, the detector arrangement in this embodiment is in accordance with the invention after the last passed scale, Z₁= 1 x (TP_M× ∩_Vernier) / Λ and n = 1 is selected.
[0038]
A schematic, not scaled illustration of this relationship is shown in FIG. 3, which is used in equations (2) and (3) in addition to measurement scale M and scan scale A. , Various geometric sizes TP_M, TP_A, ∩_Vernier, Z₁And d_VTIndicates. It is further illustrated in FIG. 3, and thus the periodic distance d_VTA suitable detector plane with sufficient contrast is obtained. As such, a vernier stripe pattern appears immediately after the last scale that is passed based on the vernier effect. However, the propagating light beam has a single propagation direction. There are various diffraction orders according to the selected scale parameters. The last passed graduation before the detector array-in this case the measurement graduation M-the diffraction order 0. Are generated in the direction of the subsequent detector array. Second and higher diffraction orders occur. The subdivision of the individual diffraction orders based on the vernier effect, which mainly produces individual partial vernier stripes due to interference, is ignored. When such a diffraction order is cut off, the same vernier stripe pattern is generated as in the case of considering all the light beams having all the superimposed diffraction orders. Each diffraction order has a partial vernier stripe pattern in the graduation direction X. On the other hand, when there is a correct superposition of the phases of the various partial vernier stripe patterns on the plane of the scale M that has been finally passed, the phase relationship subsequently changes based on different propagation directions. But the distance Z from the last scale A_nAgain has sufficient contrast vernier stripes, because partial vernier stripes of different diffraction orders are again phased correctly.
[0039]
In practice, the distance Z from the last scale T₁, Z₂The detector plane with is particularly important because, if the value of n is large, in some cases non-optimal collimated illumination is additionally negatively evaluated, i.e. the contrast is reduced.
[0040]
The effect described is very similar to the known automatic imaging of a grating known as the Talbot effect. Therefore, the above automatic imaging of the vernier fringe system is called the vernier-Talbot effect and has the magnitude d_VTIs called the vernier tarbot distance.
[0041]
Next, specific numerical values for the parameters of the second embodiment of the optical position measuring device according to the invention are given, which embodiment is likewise formed as an imaging system and is similar in basic to the example of FIG. It has a structure. In this case, the imaging system is specified in such a way that it is not necessary to separate the generated diffraction orders except for the vernier effect, because all intensity modulations worthy of the individual diffraction orders are approximately in phase. Because it will not disappear. In general, the graduation passed at the end of such an imaging system is formed as an amplitude grating.
[0042]
In a second variant of the position measuring device according to the invention, an LED or a semiconductor laser is used as the light source, which emits light with a wavelength λ = 860 nm. The optical axis of the light source is arranged to be inclined by an angle ε = 30 ° in the direction of the scale range vertical axis with respect to the normal line of the scanning plate. The light beam emitted from the light source first reaches a scanning scale on a transparent scanning plate which is formed as a phase plate and has scale areas alternately arranged in the form of webs and gaps. The phase grating of the scanning scale is TP_A= 37.04 μm, phase angle φ = π and web-scale period ratio τ = 0.5, ie the web has a gap width in the measuring direction X. After the light beam appearing on the phase grating is decomposed into various diffraction orders, the diffracted light beam reaches the reflection measurement scale. This is formed as an amplitude grating with reflective lines and non-reflective gaps arranged alternately and scale period TP_M= 20μm ≠ TP_A/ 2 as well as the line-scale period ratio τ = 0.5. From there, further light flux is reflected in the direction of the scanning plate, where it passes through the transparent window of the scanning plate and finally appears on the detector array. The vernier stripe pattern generated there is detected, and the vernier stripe pattern is a vernier period ∩ in the modification described by the equation (1)._Vernier= 1 / (2 / TP_A)-(1 / TP_M). In this case, the detector arrangement is determined from the last passed scale to Z₁= (∩_Vernier× TP_M) / Λ and can be formed similar to the embodiment according to FIG. 2, resulting in a desired number of out-of-phase scan signals on the output side. In general, the detector array is set so that three scanning signals that are 120 ° out of phase or scanning signals that are 90 ° out of phase are obtained. The signal period of the detected scanning signal is the other measurement graduation period TP in this embodiment._MIt corresponds to. For the sake of completeness in the first embodiment, both values η and β, which will be described below, are already given to this point, and η = 0 and β = 1.
[0043]
On the other hand, as described above in relation to the imaging position measuring device, the configuration according to the invention is also applied to such a system by the following description of another embodiment of the interference position measuring device. It will be revealed.
[0044]
FIG. 4 shows a schematic side view of a third embodiment of an optical position measuring device according to the invention formed as an interference position measuring device. The position measuring device further comprises a scanning unit 11 which is arranged so as to be movable in the measuring direction X with respect to the measuring rule 12, in which case the measuring rule is arranged on the measuring scale support 12.1 and on it. The measurement scale 12.2. The measuring direction X is oriented perpendicular to the drawing plane in this illustration. The light source 11.1 formed as an LED or a suitable semiconductor laser belongs to the scanning unit 11, whose optical axis is inclined by an angle ε with respect to the normal on the surface of the transparent scanning plate 11.3 in the line direction. Has been placed. The light source 11.1 is followed by a collimator optical system 11.2, and the collimator optical system is connected to a scanning scale 11.4a in which light beams are arranged on the surface of the scanning plate 11.3 in this embodiment. Before appearing on the first partial region of The scanning scale 11.4a is formed as a phase grating as in the above embodiment, and the scanning scale period TP._A= 15.75 μm, phase angle φ = π and web-scale period ratio τ = 0.5. Reference is made to the above examples for the definition of various lattice parameters. In the scanning scale 11.4a, the appearing light beam is divided into various diffraction orders, and the subsequently diffracted light beam appears on the reflection measurement scale M. The reflection measurement graduation is likewise formed as a phase grating and has a graduation period TP_M= 8μm ≠ 0.5 × TP_A, And a phase grating having a phase angle φ = π and a web-scale period ratio τ = 0.5. After reflection in the direction of the further diffracted light beam in the direction of the scanning plate 11.3, the light beam appears on the second partial area of the scanning scale, and various divided light beams are matched according to the partial area. In this case, after passing the scanning graduation 11.4b representing the last graduation,_Vernier= 1 / [(4 / TP_A)-(2 / TP_M)] Is produced. Vernier cycle ∩_VernierIs obtained from equation (1) already described above. As in the previous examples, the two values, η and β, to be explained next have already been given at this point: η = 0.5, β = 1.
[0045]
Again, in this example, a predetermined distance Z from the last graduation for correct superposition of the phases of the various partial vernier patterns propagating in different diffraction directions_nOnly the state of is important. A vernier pattern with sufficient contrast at this distance exists and can be detected by the detector array 11.5. The detector array 11.5 has a basic structure corresponding to the configuration in the example of FIG. 2 as implied. Distance Z from the last passed scale to the optical detector plane_nFor this reason, it must be taken into account that the partial vernier stripes are already out of phase with respect to each other in the plane of the graduation where it was last passed. This phase difference is the correspondingly changed distance Z_nMust be compensated by. The following formula (4) is applied to this.
[0046]
Z_n= (N + η) × d_VT                  (Formula 4)
In this case, n = 0, 1, 2, 3,.
[0047]
d_VT: Distance between adjacent detector planes or vernier tarbot planes specified by equation (3) and having sufficient contrast of vernier stripes
η: 360 ° fractional phase difference of the partial vernier stripe pattern that appears in various directions on the last passed scale, and this phase difference occurred at various points in the plane of the last passed scale It is a phase difference between diffraction orders. In the case of the above embodiment of FIG. 4, the phase difference is 180 °, ie η is η = 0.5; generally 0 ≦ η <1.
[0048]
Value d_VTI.e., because of the vernier Talbot distance, in this example d_VT= (∩_Vernier× TP_M) / Λ. Thus, immediately after the last passed scale, according to equation (4), no or only slight modulation of the scanning signal or only slight contrast of the vernier pattern is expected. The first possible detector plane is 0 ≦ η <1 and n = 0, thus the distance Z₀To occur.
[0049]
In general, according to the present invention, η = 0 and n> 0 are selected in the imaging system, whereas η ≠ 0 and n = 0, 1, 2, 3,.
[0050]
Unlike the illustrated embodiment, the scanning graduations 11.4a and 11.4b are not arranged on the upper surface of the scanning plate 11.3 facing the light source, and the scanning graduation 11.4b .3 measuring scale 12.2 is arranged on the lower surface facing the measuring plate 12.3, by suitable selection of the thickness of the scanning plate 11.3, the detector array 11.5 is directly above the scanning plate 11.3. This corresponds to the case of n = 0. In such an embodiment, contact of the detector array 11.5 on the scanning plate 11.3 is also possible. This can be done, for example, by known chip-on-glass-technology and / or flip-chip technology.
[0051]
The signal period SP of the detected scanning signal is the other normal measurement scale TP in this embodiment._MHalf, ie SP = TP_M/ 2 = corresponds to 4 μm.
[0052]
Next, a modified form of the embodiment of FIG. 4 will be described, i.e. a fourth embodiment of the invention formed as an interference system will be described. The scanning gratings 11.4a and 11.4b are newly formed as phase gratings and have a graduation period TP._A= 8 μm, phase angle φ = (2/3) and web-scale period ratio τ = 0.34. Measurement scale 12.2 is scale period TP_M= 7.874 μm ≠ TP_A, Phase angle φ = π and web-scale period ratio τ = 0.5. Vernier cycle ∩_VernierIs （from equation (1)_Vernier= 1 / [(2 / TP_A)-(2 / TP_M)]. In this case, the value η is η = 1/3. The value β to be explained next is further β = 1.
[0053]
Another embodiment of the apparatus for measuring optical position by interference according to the present invention is thus collectively illustrated in FIG. The illustrated position measuring device further includes a scanning unit 21 which is arranged so as to be movable in the measuring direction X with respect to the measuring scale 22.2. In this case, the measuring direction X is again oriented perpendicularly to the drawing plane. It has been. In a particularly advantageous embodiment, the measuring scale 22.2 is formed as a flexible strip measuring scale. A light source 21. 1 formed as an LED or a suitable semiconductor laser is provided on the scanning unit 21 side, and its optical axis is inclined with respect to the surface of the transparent scanning plate 21.3 by an angle ε. . The light source 21. 1 is arranged following the collimator optical system, and the collimator optical system has a light source 21.1 before the light beam passes through the transparent and optically ineffective area of the scanning plate 21.3. Transmits the luminous flux emitted from. After passing through the scanning plate 21. 3, the light beam reaches the measurement graduation 22.2 formed as a reflection phase grating for the first time. The measurement scale is scale period TP_M= 16 μm, phase angle φ = π and web-scale period ratio τ = 0.5. The light beam from the measurement graduation 22.2 is reflected in the direction of the scanning plate 21.3 onto the scanning graduation 21.4, and the scanning graduation is disposed inside the upper surface of the scanning plate 21.3. ing. The provided scanning scale 21.4 has a scale period TP._A= 7.874 μm ≠ 0.5 x TP_MThe phase grating is formed as a reflecting phase grating having a phase angle φ = π and a web-scale period ratio τ = 0.5. Regarding the definition of various lattice parameters, the above embodiment is referred to again. The light beam diffracted by the scanning graduation 21.4 is reflected in the direction of the measurement graduation 22.2 and then the second reflection is further performed in the direction of the scanning plate 21.3. The scanning plate 21. 3 has a transparent area defined by the luminous flux coming from the measuring scale 22.2 before the vernier stripe pattern produced according to the last passing scale 22.2 is detected via the detector array 21.5. Is passed. The detector array is arranged according to the invention on a further preferred detector plane. The vernier stripe pattern detected at that time_VernierWith a vernier period ∩_VernierAccording to equation (1)_Vernier= 1 / [(4 / TP_A)-(2 / TP_M)] Is obtained from the above formula (3). Further, β = 1 and η = 1/2.
[0054]
Distance Z from the last graduation leading to phase-matching of various partial vernier stripes_nOn the other hand, also in this case, η = ½ in the above equation (4). Correspondingly, the detector array 22.5 and the like are arranged in this plane. Furthermore, if there is a measurement scale 22.2 immediately after the last passed scale, only a slight modulation of the detected scanning signal is expected. The first fundamentally possible scan plane with n = 0 proves to be likewise not optimal in this configuration, because the possible scan planes are the measurement graduation 22 and the scan plate 21 for a given parameter. This is because it is located between. For this reason, the detector array 21.5 in the detector plane has a distance Z from the last passed scale.₁= 1) is positioned in the detector plane, where a sufficient contrast vernier stripe pattern is detected according to the invention. In this embodiment, the signal period SP of the detected scanning signal is SP = TP._M/ 4.
[0055]
In another variant of the embodiment according to FIG. 5, ie in the sixth example of the invention, the following parameters are selected: Scale period TP with respect to measurement scale 22.2 formed as a phase grating_M≠ TP_AThe phase angle φ = 2 / 3π and the web-scale period ratio τ≈0.34 are applied. Similarly, TP is used as a scanning scale 21.4 formed as a phase grating._A≠ TP_MThe phase angle φ = π and the web-scale period ratio τ≈0.5 and further β = 1, η = 1/3 are applied.
[0056]
There are various possibilities for the arrangement of the scanning scale 21.4 on the side of the scanning plate 21.3. If the scanning scale 21.4 can be arranged directly on the upper surface of the scanning plate 21.3, this leads to the possibility of slight contamination. Similarly, however, it is also possible to arrange the scanning scale 21.4 on the side of the scanning plate 21.3 facing the measuring scale by selecting the corresponding thickness of the scanning plate 21.3. In this variant, the detector array 21.5 can be arranged directly on the upper surface of the scanning plate 21.3.
[0057]
Next, another implementation variant of the optical position measuring device based on the concept according to the present invention will be described. For example, the measurement scale 22.2 in the embodiment of FIG. 5 can be arranged in a curved shape inside or outside the rotating cylinder. At this time, the rotation axis of the cylinder is directed in the Y direction. In such a variant, the enlargement or reduction in the detector plane of the vernier pattern to be scanned is performed on the basis of the curved arrangement of the measurement scale 22.2. When the measuring scale is arranged on the outer surface of the cylinder, expansion is performed, and when it is arranged on the inner surface of the cylinder, corresponding reduction is performed. This optical effect is the same as in the case of a curved measurement scale, as in all other cases with an optical path that is not collimated due to optical elements that are arbitrarily focused or diffused in the optical path, for example ( The case of a curved measurement scale in 3) is considered. For this purpose, an enlargement factor or correction factor β is introduced which depicts the transmission and expansion of the partial vernier pattern period from the last graduation point passed through the transmission or expansion of the partial vernier pattern period to the detector plane. The Therefore, the general formula (3) is obtained.
[0058]
d_VT= (Β × ∩_Vernier× TP_eff) / Λ (Formula 3)
Or d_VT= Β × d_VT0At that time
d_VT0= (∩_Vernier× TP_eff) / Λ
And
∩_Vernier: The vernier period of the partial vernier stripe pattern at the last passage of the scale.
[0059]
The enlargement factor β spread on the general equation (3 ′) naturally depends on the predetermined geometric value inside the position measuring device according to the invention. In this connection, reference is made to FIG. 6, which serves to explain the important values for which the factors are specified. Figure 6 shows the vernier stripe pattern_VernierIn addition to the last passed scale T, in which the partial vernier stripe pattern having the position is in the plane, the distance Z from the scale T_nA detector plane is shown, and there is a vernier stripe pattern magnified by a factor β based on the diffused light flux present in the detector plane. Furthermore, the point Q shown in FIG. 6 is regarded as a virtual light source point or a real light source point having a luminous flux or a vernier stripe pattern in this case. Therefore the distance Z_QGives the distance of the real or imaginary light source point from the last passed scale T. In the case of β> 1, that is, when the vernier stripe pattern is enlarged, the distance Z_QIs Z_Q> 0; if β <1, that is, Z_Q<0. According to the principle of the central interval, for such a geometric dimension, the enlargement factor or correction factor β is:
[0060]
β = (Z_n+ Z_Q) / Z_Q
In the case of the above selection of the measurement scale arrangement on the cylinder outer surface, the factor β> 1 is selected, whereas in the case of the measurement scale arrangement on the cylinder inner surface, β <1 is selected.
[0061]
From equation (4) as well as the above described equation (3 ′), all equations (5) valid for the system according to the invention apply and from this equation (5) the position of the detector plane or finally Distance Z from the passed scale_QIs required.
[0062]
1 / Z_n+ 1 / Z_Q= 1 / [(n + η) × d_VT0] (Formula 5)
Value Z in equation (5)_QThe meaning of n, η has already been explained above. Similarly the value d_VT0The definition of_VernierIntervenes. On the other hand, in the imaging system discussed, in the case of non-collimated illumination or when optical elements are used in the optical path, the optical path affects the diffusion of the luminous flux and_VernierA clear analytical expression is not possible, similar to equation (1). Vernier cycle ∩_VernierIs given only by relationships that are specifically adapted to the optical conditions. Selective vernier cycle in such a system selectively_VernierCan be identified by a numerical method such as so-called “ray tracing.” Therefore, basically, at the point of the scale that was last passed under the vernier period in the general formula (5), The period of the partial vernier stripe pattern is understood.
[0063]
Equation (5) is effective for both non-collimated illumination and collimated illumination as described above. Value Z for collimated lighting_QIs Z_Q= ∞, i.e., β = 1, so equation (5) is identical to equation (4) above. Conversely, for non-collimated illumination, the value Z_QFinally, ie Z_Q≠ ∞ and β ≠ = 1.
[0064]
Then the value Z_QIs Z in equation (5)_Q= (N + η) × d_VT0Where n = 1, 2,... Is described. The vernier stripe pattern is the distance Z from the last scale that was passed_nOccurs at ∞. In practice, the detector array must be positioned in the focal plane of the focusing lens following the subsequent graduation.
[0065]
Basically, of course, the last passed graduation is followed by a so-called relay optical system, which produces an image of the detector plane obtained in equation (5) in another plane.
[0066]
Subsequently, equation (5) introduced in the case of the interference system is also applied to the imaging position measuring device in the corresponding selection of the value η, in this case selecting η = 0.
[0067]
This is due to the fact that equations (3 ') and (5) above have general validity and that the corresponding selection of different parameters makes it possible to modify the imaging and interference variations described for the optical position measuring device according to the invention. Can be specifically described. These equations then also describe the known case of an optical position measuring device such as an imaging system according to the German patent application 19527287 mentioned at the beginning. There, the detector plane is positioned and the resulting vernier pattern is detected almost immediately after the last passed graduation, ie the parameters n and η are n≈0 and η = 0 in such a position measuring device. Is selected. The parameters n and η in equations (3) and (5) that are generally valid for the optical position measuring device according to the invention are selected such that n> 0 or η≈0.
[0068]
Essentially at this point there is of course some tolerance for the exact position of each detector plane. Even if there is a slight deviation from the ideal position obtained by the above equation, sufficient intensity modulation can be achieved in some cases.
[0069]
Furthermore, within the scope of the present invention, for example, when one of the used graduations is formed as a two-dimensional graduation and thus produces a transverse diffraction order biased in the direction of the moire fringes, the measurement direction of the so-called moire fringe shape It is also possible to detect a periodic stripe pattern that passes vertically. The generation of moiré fringes selectively is of course achieved in a known manner and manner, with the graduations used being twisted together by a predetermined angle.
[0070]
Thus, there are a series of possibilities that the present invention can be formed in various embodiments. Accordingly, the above description of the embodiments will, of course, not reach a complete understanding of the inventive idea.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic configuration of a first embodiment of a position measuring apparatus according to the present invention, which is formed as an imaging position measuring apparatus.
FIG. 2 is a diagram representing the detector plane of an embodiment of the optical position measuring device according to the invention according to FIG. 1 in association with a scanned vernier pattern.
FIG. 3 is a schematic diagram for explaining the relationship with the optimum positioning of the detector plane in the position measuring device to be imaged;
FIG. 4 is a schematic view of a third embodiment of a position measuring device according to the invention, formed as an interference position measuring device.
FIG. 5 is a schematic view of a fifth embodiment of a position measuring device according to the invention, formed as an interference position measuring device.
FIG. 6 is a schematic diagram for explaining a situation in the case of non-collimated illumination.
[Explanation of symbols]
1 Scanning unit
1.1 Light source
1.4 Scanning scale
1.5 Detector array
2.2 Measurement scale
11 Scanning unit
11.1 Light source
11.4a Scanning scale
11.4b Scanning scale
11.5 Detector array
12.2 Measurement scale
21 Scanning unit
21.1 Light source
21.4 Scanning scale
21.5 Detector array
22.2 Measurement scale

Claims (11)

In an optical position measuring device for determining the relative position of two objects movable relative to each other in the measuring direction,
a) at least one periodic measurement scale (2.2; 12.2; 22.2) associated with one of the objects;
b) a scanning unit (1; 11; 21) coupled to the other object;
The scanning unit
b1) a light source (1.1; 11.1; 21.1);
b2) at least one scanning scale (1.4; 11.4a; 11.4b; 21.4);
b3) a detector array (1.5; 11.5; 21.5) in the detector plane, the detector array being a luminous flux emitted from a light source (1.1; 11.1; 21.1) Consists of a plurality of photosensitive detector elements (D1,... D20) for scanning periodic fringes resulting from the interaction with different scales, the detector plane being a detector array Finally the light beam is disposed at a distance Z _n from the scale that has passed and the distance Z _n the following relationship before entering, i.e. _{1 / Z n + 1 / Z} Q = 1 / [(n + η) × d _VTO]
Where Z _Q is the distance from the periodic or striped real or virtual light source point to the graduation through which the beam last passed before entering the detector array, n = 0, 1, 2, 3, ...
η: a phase difference of a 360 ° fraction of a periodic striped pattern appearing in different directions on the graduation through which the light beam finally passed before entering the detector array, and at least n> 0 or η ≠ 0 is selected And 0 <η <1, n + η ≠ 0, Z _Q ≠ 0, and d _VTO = (TP _eff × ∩ _Vernier ) / λ,
TP _eff : Effective graduation period of the scanning array, which occurs on the scale where the light beam last passed before entering the detector array and correctly draws the directions of 0th order and ± 1st order diffraction having sufficient intensity,
λ = light wavelength of the light source used,
∩ _Vernier : The optical position measuring device according to claim 1, wherein the optical position measuring device has a period of a periodic stripe pattern at a position of a scale where a light beam has finally passed before entering the detector array. In this case, the detector elements (D1 to D20) are arranged adjacent to each other in the form of blocks in the measuring direction (X), in which case at least two blocks (B1,... B5) are provided and the blocks ( B1, · · B5) per each of k individual detector elements (D1~D20) is, the distance is disposed inwardly of the beta × ∩ _Vernier, here _{β = (Z Q + Z n} ) / Z _Q and then the detector elements (D1 to D20) are further out of phase by 360 ° / k during scanning from the adjacent detector elements (D1 to D20) of each block (B1,... B5) 2. The optical position measuring device according to claim 1, wherein the optical position measuring device is arranged so as to obtain scanning signals (A ₀ , A ₉₀ , A ₁₈₀ , A ₂₇₀ ).   3. The optical position measuring device according to claim 2, wherein detector elements (D1... D20) of different blocks (B1... B5) that emit output signals of the same phase are connected to each other. Because of the distance d _VT between adjacent detector planes,
d _VT = β × d _VTO
The optical position measuring device according to claim 1, wherein β = (Z _Q + Z _n ) / Z _Q. The optical position measuring device according to claim 1, wherein collimated illumination with Z _Q = ∞ and β = 1 is provided. 2. The optical position measuring device according to claim 1, wherein collimated illumination with Z _Q ≠ ∞ and β ≠ 1 is provided.     The optical position measuring device according to claim 1, wherein η = 0 and n> 0 are selected.     The optical position measuring device according to claim 1, wherein η ≠ 0 and n = 0, 1, 2, 3,. Scanning unit (1) is a transparent scanning plate with a scanning graduation (1.4) of the scanning graduation period TP _A has a (1.3), the light flux emitted from the result the light source (1.1), first through scanning graduation (1.4), then appears on the measuring graduation to reflect the measuring graduation period TP _M (2.2), where reflection takes place in the direction of the scanning plate (1.3) and reflected 2. The optical position measuring device according to claim 1, wherein the luminous flux passes through a scanning plate (1.3) adjacent to the scanning scale (1.4) and reaches a detector array in the detector plane. Scanning unit (11) has a transparent scanning plate with a scanning graduation scanning graduation period TP _A (1.4) (11.3), the light flux emitted from the result the light source (11.1), first reaches a first partial region of the scanning graduation (11.4 a), and then appears on the measuring graduation to reflect the measuring graduation period TP _M (12.2), where reflection is, in the direction of the scanning plate (1.3) The reflected and reflected light flux appears in the second partial area of the scan graduation (11.4a) and before reaching the detector array (11.5) in the detector plane, the second of the scan graduation (11.4a). 2. The optical position measuring device according to claim 1, wherein the optical position measuring device transmits two partial regions. Scanning unit (21) has a transparent scanning plate (21.3), of a scanning graduation (the 21.4) and the measuring graduation period TP _M for reflecting the transparent scanning plate measuring graduation period TP _A The scanning plate (21) facing the reflective measuring graduation (22.2) configured in the same way, so that the light emitted from the light source (21.1) is first adjacent to the scanning graduation (21.4). .3) is transmitted there and reflected in the direction of the scanning graduation (21.4), from which the reflection in the direction of the measuring graduation (22.2) is directed to the scanning plate (21.3). Before the reflected beam passes through the scanning plate (21.3) adjacent to the scanning scale (21.4) and reaches the detector array (21.5) in the detector plane, The optical position measuring device according to claim 1.

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